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            <ol class="chapter"><li class="affix"><a href="../../../introduction.html">Introduction</a></li><li class="spacer"></li><li><a href="../../../examples/index.html"><strong aria-hidden="true">1.</strong> Examples</a></li><li><ol class="section"><li><a href="../../../examples/hello-world.html"><strong aria-hidden="true">1.1.</strong> Hello, World!</a></li><li><a href="../../../examples/console-log.html"><strong aria-hidden="true">1.2.</strong> Using console.log</a></li><li><a href="../../../examples/add.html"><strong aria-hidden="true">1.3.</strong> Small Wasm files</a></li><li><a href="../../../examples/without-a-bundler.html"><strong aria-hidden="true">1.4.</strong> Without a Bundler</a></li><li><a href="../../../examples/synchronous-instantiation.html"><strong aria-hidden="true">1.5.</strong> Synchronous Instantiation</a></li><li><a href="../../../examples/import-js.html"><strong aria-hidden="true">1.6.</strong> Importing functions from JS</a></li><li><a href="../../../examples/char.html"><strong aria-hidden="true">1.7.</strong> Working with char</a></li><li><a href="../../../examples/wasm-in-wasm.html"><strong aria-hidden="true">1.8.</strong> js-sys: WebAssembly in WebAssembly</a></li><li><a href="../../../examples/dom.html"><strong aria-hidden="true">1.9.</strong> web-sys: DOM hello world</a></li><li><a href="../../../examples/closures.html"><strong aria-hidden="true">1.10.</strong> web-sys: Closures</a></li><li><a href="../../../examples/performance.html"><strong aria-hidden="true">1.11.</strong> web-sys: performance.now</a></li><li><a href="../../../examples/fetch.html"><strong aria-hidden="true">1.12.</strong> web-sys: using fetch</a></li><li><a href="../../../examples/weather_report.html"><strong aria-hidden="true">1.13.</strong> web-sys: Weather report</a></li><li><a href="../../../examples/2d-canvas.html"><strong aria-hidden="true">1.14.</strong> web-sys: canvas hello world</a></li><li><a href="../../../examples/julia.html"><strong aria-hidden="true">1.15.</strong> web-sys: canvas Julia set</a></li><li><a href="../../../examples/web-audio.html"><strong aria-hidden="true">1.16.</strong> web-sys: WebAudio</a></li><li><a href="../../../examples/webgl.html"><strong aria-hidden="true">1.17.</strong> web-sys: WebGL</a></li><li><a href="../../../examples/websockets.html"><strong aria-hidden="true">1.18.</strong> web-sys: WebSockets</a></li><li><a href="../../../examples/webrtc_datachannel.html"><strong aria-hidden="true">1.19.</strong> web-sys: WebRTC DataChannel</a></li><li><a href="../../../examples/request-animation-frame.html"><strong aria-hidden="true">1.20.</strong> web-sys: requestAnimationFrame</a></li><li><a href="../../../examples/paint.html"><strong aria-hidden="true">1.21.</strong> web-sys: A Simple Paint Program</a></li><li><a href="../../../examples/wasm-in-web-worker.html"><strong aria-hidden="true">1.22.</strong> web-sys: Wasm in Web Worker</a></li><li><a href="../../../examples/raytrace.html"><strong aria-hidden="true">1.23.</strong> Parallel Raytracing</a></li><li><a href="../../../examples/wasm-audio-worklet.html"><strong aria-hidden="true">1.24.</strong> Wasm Audio Worklet</a></li><li><a href="../../../examples/todomvc.html"><strong aria-hidden="true">1.25.</strong> web-sys: A TODO MVC App</a></li></ol></li><li><a href="../../../reference/index.html"><strong aria-hidden="true">2.</strong> Reference</a></li><li><ol class="section"><li><a href="../../../reference/deployment.html"><strong aria-hidden="true">2.1.</strong> Deployment</a></li><li><a href="../../../reference/js-snippets.html"><strong aria-hidden="true">2.2.</strong> JS snippets</a></li><li><a href="../../../reference/static-js-objects.html"><strong aria-hidden="true">2.3.</strong> Static JS Objects</a></li><li><a href="../../../reference/passing-rust-closures-to-js.html"><strong aria-hidden="true">2.4.</strong> Passing Rust Closures to JS</a></li><li><a href="../../../reference/receiving-js-closures-in-rust.html"><strong aria-hidden="true">2.5.</strong> Receiving JS Closures in Rust</a></li><li><a href="../../../reference/js-promises-and-rust-futures.html"><strong aria-hidden="true">2.6.</strong> Promises and Futures</a></li><li><a href="../../../reference/iterating-over-js-values.html"><strong aria-hidden="true">2.7.</strong> Iterating over JS Values</a></li><li><a href="../../../reference/arbitrary-data-with-serde.html"><strong aria-hidden="true">2.8.</strong> Arbitrary Data with Serde</a></li><li><a href="../../../reference/accessing-properties-of-untyped-js-values.html"><strong aria-hidden="true">2.9.</strong> Accessing Properties of Untyped JS Values</a></li><li><a href="../../../reference/working-with-duck-typed-interfaces.html"><strong aria-hidden="true">2.10.</strong> Working with Duck-Typed Interfaces</a></li><li><a href="../../../reference/cli.html"><strong aria-hidden="true">2.11.</strong> Command Line Interface</a></li><li><a href="../../../reference/optimize-size.html"><strong aria-hidden="true">2.12.</strong> Optimizing for Size</a></li><li><a href="../../../reference/rust-targets.html"><strong aria-hidden="true">2.13.</strong> Supported Rust Targets</a></li><li><a href="../../../reference/browser-support.html"><strong aria-hidden="true">2.14.</strong> Supported Browsers</a></li><li><a href="../../../reference/weak-references.html"><strong aria-hidden="true">2.15.</strong> Support for Weak References</a></li><li><a href="../../../reference/reference-types.html"><strong aria-hidden="true">2.16.</strong> Support for Reference Types</a></li><li><a href="../../../reference/types.html"><strong aria-hidden="true">2.17.</strong> Supported Types</a></li><li><ol class="section"><li><a href="../../../reference/types/imported-js-types.html"><strong aria-hidden="true">2.17.1.</strong> Imported JavaScript Types</a></li><li><a href="../../../reference/types/exported-rust-types.html"><strong aria-hidden="true">2.17.2.</strong> Exported Rust Types</a></li><li><a href="../../../reference/types/jsvalue.html"><strong aria-hidden="true">2.17.3.</strong> JsValue</a></li><li><a href="../../../reference/types/boxed-slices.html"><strong aria-hidden="true">2.17.4.</strong> Box&lt;[T]&gt; and Vec<T></a></li><li><a href="../../../reference/types/pointers.html"><strong aria-hidden="true">2.17.5.</strong> *const T and *mut T</a></li><li><a href="../../../reference/types/non-null.html"><strong aria-hidden="true">2.17.6.</strong> NonNull<T></a></li><li><a href="../../../reference/types/numbers.html"><strong aria-hidden="true">2.17.7.</strong> Numbers</a></li><li><a href="../../../reference/types/bool.html"><strong aria-hidden="true">2.17.8.</strong> bool</a></li><li><a href="../../../reference/types/char.html"><strong aria-hidden="true">2.17.9.</strong> char</a></li><li><a href="../../../reference/types/str.html"><strong aria-hidden="true">2.17.10.</strong> str</a></li><li><a href="../../../reference/types/string.html"><strong aria-hidden="true">2.17.11.</strong> String</a></li><li><a href="../../../reference/types/number-slices.html"><strong aria-hidden="true">2.17.12.</strong> Number Slices</a></li><li><a href="../../../reference/types/boxed-number-slices.html"><strong aria-hidden="true">2.17.13.</strong> Boxed Number Slices</a></li><li><a href="../../../reference/types/result.html"><strong aria-hidden="true">2.17.14.</strong> Result&lt;T, E&gt;</a></li></ol></li><li><a href="../../../reference/attributes/index.html"><strong aria-hidden="true">2.18.</strong> #[wasm_bindgen] Attributes</a></li><li><ol class="section"><li><a href="../../../reference/attributes/on-js-imports/index.html"><strong aria-hidden="true">2.18.1.</strong> On JavaScript Imports</a></li><li><ol class="section"><li><a href="../../../reference/attributes/on-js-imports/catch.html" class="active"><strong aria-hidden="true">2.18.1.1.</strong> catch</a></li><li><a href="../../../reference/attributes/on-js-imports/constructor.html"><strong aria-hidden="true">2.18.1.2.</strong> constructor</a></li><li><a href="../../../reference/attributes/on-js-imports/extends.html"><strong aria-hidden="true">2.18.1.3.</strong> extends</a></li><li><a href="../../../reference/attributes/on-js-imports/getter-and-setter.html"><strong aria-hidden="true">2.18.1.4.</strong> getter and setter</a></li><li><a href="../../../reference/attributes/on-js-imports/final.html"><strong aria-hidden="true">2.18.1.5.</strong> final</a></li><li><a href="../../../reference/attributes/on-js-imports/indexing-getter-setter-deleter.html"><strong aria-hidden="true">2.18.1.6.</strong> indexing_getter, indexing_setter, and indexing_deleter</a></li><li><a href="../../../reference/attributes/on-js-imports/js_class.html"><strong aria-hidden="true">2.18.1.7.</strong> js_class = &quot;Blah&quot;</a></li><li><a href="../../../reference/attributes/on-js-imports/js_name.html"><strong aria-hidden="true">2.18.1.8.</strong> js_name</a></li><li><a href="../../../reference/attributes/on-js-imports/js_namespace.html"><strong aria-hidden="true">2.18.1.9.</strong> js_namespace</a></li><li><a href="../../../reference/attributes/on-js-imports/method.html"><strong aria-hidden="true">2.18.1.10.</strong> method</a></li><li><a href="../../../reference/attributes/on-js-imports/module.html"><strong aria-hidden="true">2.18.1.11.</strong> module = &quot;blah&quot;</a></li><li><a href="../../../reference/attributes/on-js-imports/raw_module.html"><strong aria-hidden="true">2.18.1.12.</strong> raw_module = &quot;blah&quot;</a></li><li><a href="../../../reference/attributes/on-js-imports/no_deref.html"><strong aria-hidden="true">2.18.1.13.</strong> no_deref</a></li><li><a href="../../../reference/attributes/on-js-imports/static_method_of.html"><strong aria-hidden="true">2.18.1.14.</strong> static_method_of = Blah</a></li><li><a href="../../../reference/attributes/on-js-imports/structural.html"><strong aria-hidden="true">2.18.1.15.</strong> structural</a></li><li><a href="../../../reference/attributes/on-js-imports/typescript_type.html"><strong aria-hidden="true">2.18.1.16.</strong> typescript_type</a></li><li><a href="../../../reference/attributes/on-js-imports/variadic.html"><strong aria-hidden="true">2.18.1.17.</strong> variadic</a></li><li><a href="../../../reference/attributes/on-js-imports/vendor_prefix.html"><strong aria-hidden="true">2.18.1.18.</strong> vendor_prefix</a></li></ol></li><li><a href="../../../reference/attributes/on-rust-exports/index.html"><strong aria-hidden="true">2.18.2.</strong> On Rust Exports</a></li><li><ol class="section"><li><a href="../../../reference/attributes/on-rust-exports/constructor.html"><strong aria-hidden="true">2.18.2.1.</strong> constructor</a></li><li><a href="../../../reference/attributes/on-rust-exports/js_name.html"><strong aria-hidden="true">2.18.2.2.</strong> js_name = Blah</a></li><li><a href="../../../reference/attributes/on-rust-exports/js_class.html"><strong aria-hidden="true">2.18.2.3.</strong> js_class = Blah</a></li><li><a href="../../../reference/attributes/on-rust-exports/readonly.html"><strong aria-hidden="true">2.18.2.4.</strong> readonly</a></li><li><a href="../../../reference/attributes/on-rust-exports/skip.html"><strong aria-hidden="true">2.18.2.5.</strong> skip</a></li><li><a href="../../../reference/attributes/on-rust-exports/skip_jsdoc.html"><strong aria-hidden="true">2.18.2.6.</strong> skip_jsdoc</a></li><li><a href="../../../reference/attributes/on-rust-exports/start.html"><strong aria-hidden="true">2.18.2.7.</strong> start</a></li><li><a href="../../../reference/attributes/on-rust-exports/main.html"><strong aria-hidden="true">2.18.2.8.</strong> main</a></li><li><a href="../../../reference/attributes/on-rust-exports/typescript_custom_section.html"><strong aria-hidden="true">2.18.2.9.</strong> typescript_custom_section</a></li><li><a href="../../../reference/attributes/on-rust-exports/getter-and-setter.html"><strong aria-hidden="true">2.18.2.10.</strong> getter and setter</a></li><li><a href="../../../reference/attributes/on-rust-exports/inspectable.html"><strong aria-hidden="true">2.18.2.11.</strong> inspectable</a></li><li><a href="../../../reference/attributes/on-rust-exports/skip_typescript.html"><strong aria-hidden="true">2.18.2.12.</strong> skip_typescript</a></li><li><a href="../../../reference/attributes/on-rust-exports/getter_with_clone.html"><strong aria-hidden="true">2.18.2.13.</strong> getter_with_clone</a></li><li><a href="../../../reference/attributes/on-rust-exports/unchecked_type.html"><strong aria-hidden="true">2.18.2.14.</strong> unchecked_return_type and unchecked_param_type</a></li><li><a href="../../../reference/attributes/on-rust-exports/description.html"><strong aria-hidden="true">2.18.2.15.</strong> return_description and param_description</a></li></ol></li></ol></li></ol></li><li><a href="../../../web-sys/index.html"><strong aria-hidden="true">3.</strong> web-sys</a></li><li><ol class="section"><li><a href="../../../web-sys/using-web-sys.html"><strong aria-hidden="true">3.1.</strong> Using web-sys</a></li><li><a href="../../../web-sys/cargo-features.html"><strong aria-hidden="true">3.2.</strong> Cargo Features</a></li><li><a href="../../../web-sys/function-overloads.html"><strong aria-hidden="true">3.3.</strong> Function Overloads</a></li><li><a href="../../../web-sys/type-translations.html"><strong aria-hidden="true">3.4.</strong> Type Translations</a></li><li><a href="../../../web-sys/inheritance.html"><strong aria-hidden="true">3.5.</strong> Inheritance</a></li><li><a href="../../../web-sys/unstable-apis.html"><strong aria-hidden="true">3.6.</strong> Unstable APIs</a></li></ol></li><li><a href="../../../wasm-bindgen-test/index.html"><strong aria-hidden="true">4.</strong> Testing with wasm-bindgen-test</a></li><li><ol class="section"><li><a href="../../../wasm-bindgen-test/usage.html"><strong aria-hidden="true">4.1.</strong> Usage</a></li><li><a href="../../../wasm-bindgen-test/asynchronous-tests.html"><strong aria-hidden="true">4.2.</strong> Writing Asynchronous Tests</a></li><li><a href="../../../wasm-bindgen-test/browsers.html"><strong aria-hidden="true">4.3.</strong> Testing in Headless Browsers</a></li><li><a href="../../../wasm-bindgen-test/continuous-integration.html"><strong aria-hidden="true">4.4.</strong> Continuous Integration</a></li><li><a href="../../../wasm-bindgen-test/coverage.html"><strong aria-hidden="true">4.5.</strong> Coverage (Experimental)</a></li></ol></li><li><a href="../../../contributing/index.html"><strong aria-hidden="true">5.</strong> Contributing to wasm-bindgen</a></li><li><ol class="section"><li><a href="../../../contributing/testing.html"><strong aria-hidden="true">5.1.</strong> Testing</a></li><li><a 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href="../../../contributing/design/describe.html"><strong aria-hidden="true">5.2.7.</strong> Types in wasm-bindgen</a></li></ol></li><li><a href="../../../contributing/js-sys/index.html"><strong aria-hidden="true">5.3.</strong> js-sys</a></li><li><ol class="section"><li><a href="../../../contributing/js-sys/testing.html"><strong aria-hidden="true">5.3.1.</strong> Testing</a></li><li><a href="../../../contributing/js-sys/adding-more-apis.html"><strong aria-hidden="true">5.3.2.</strong> Adding More APIs</a></li></ol></li><li><a href="../../../contributing/web-sys/index.html"><strong aria-hidden="true">5.4.</strong> web-sys</a></li><li><ol class="section"><li><a href="../../../contributing/web-sys/overview.html"><strong aria-hidden="true">5.4.1.</strong> Overview</a></li><li><a href="../../../contributing/web-sys/testing.html"><strong aria-hidden="true">5.4.2.</strong> Testing</a></li><li><a href="../../../contributing/web-sys/logging.html"><strong aria-hidden="true">5.4.3.</strong> Logging</a></li><li><a href="../../../contributing/web-sys/supporting-more-web-apis.html"><strong aria-hidden="true">5.4.4.</strong> Supporting More Web APIs</a></li></ol></li><li><a href="../../../contributing/publishing.html"><strong aria-hidden="true">5.5.</strong> Publishing</a></li><li><a href="../../../contributing/team.html"><strong aria-hidden="true">5.6.</strong> Team</a></li></ol></li></ol>
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                        <h1 class="menu-title">The `wasm-bindgen` Guide</h1> 

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                        <a class="header" href="#catch" id="catch"><h1><code>catch</code></h1></a>
<p>The <code>catch</code> attribute allows catching a JavaScript exception. This can be
attached to any imported function or method, and the function must return a
<code>Result</code> where the <code>Err</code> payload is a <code>JsValue</code>:</p>
<pre><pre class="playpen"><code class="language-rust">
# #![allow(unused_variables)]
#fn main() {
#[wasm_bindgen]
extern &quot;C&quot; {
    // `catch` on a standalone function.
    #[wasm_bindgen(catch)]
    fn foo() -&gt; Result&lt;(), JsValue&gt;;

    // `catch` on a method.
    type Zoidberg;
    #[wasm_bindgen(catch, method)]
    fn woop_woop_woop(this: &amp;Zoidberg) -&gt; Result&lt;u32, JsValue&gt;;
}
#}</code></pre></pre>
<p>If calling the imported function throws an exception, then <code>Err</code> will be
returned with the exception that was raised. Otherwise, <code>Ok</code> is returned with
the result of the function.</p>
<blockquote>
<p>By default <code>wasm-bindgen</code> will take no action when Wasm calls a JS function
which ends up throwing an exception. The Wasm spec right now doesn't support
stack unwinding and as a result Rust code <strong>will not execute destructors</strong>.
This can unfortunately cause memory leaks in Rust right now, but as soon as
Wasm implements catching exceptions we'll be sure to add support as well!</p>
</blockquote>

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